Interop Gen: Support Overloading

[nikeokoronkwo]

This issue is to add support for overloading declarations.

This involves supporting the overloading of interfaces, classes, functions etc:

// assuming the given interfaces are specified
function clone(animal: Dog): Dog;
function clone(animal: Cat): Cat;
function clone(animal: Sheep): Sheep;
function clone(animal: Animal): Animal;

// interface overloading
interface Overloader<T extends Overloadee> {
  /* some decls */
}
interface Overloader<T extends Overloadee> {
  /* some other decls */
  getOverloadee(): Overloadee
}

This issue would involve working with declarations of the same name both during transformation and generation. Referrable declarations such as namespaces, interfaces, etc are merged together, while functions are overloaded as normal with multiple declarations.

In the case of an interface and namespace (i.e Deno's version of rm in node:fs), the namespace is named initially and the functions separately.